Jet valve pressure staging device



' Dec. 22, 1964 A. A. PERACCHIO JET VALVE PRESSURE STAGING DEVICE FiledDec. 31, 1962 2 Sheets-Sheet 1 Dec. 22, 1964 A. A. PERACCHIO 3,162,749

JET VALVE PRESSURE STAGING DEVICE Filed Dec. :51, 1962 2 Sheets-Sheet 2-Wae/f P/ECE CZ WWW United States Patent Ofiice 3,162,749 Patented Dec.22, 1964 3,162,749 JET VALVE PRESSURE STAGING DEVICE Aldo A. Peracchio,Wapping, Conn., assignor to United Aircraft Corporation, East Hartford,Conn., a corporation of Delaware Filed Dec. 31, 1962, Ser. No. 248,315 8Claims. (Cl. 219121) My invention relates to working materials with abeam of charged particles. More particularly, my invention is directedto permitting a beam of charged particles, which is generated in a firstlow pressure chamber, to impinge upon a workpiece which is located in aregion where the ambient pressure is relatively high.

While not limited thereto, my invention is thought to have particularutility when used in conjunction with an electron beam machine. Electronbeam machines, as they are commonly known, are devices which use thekinetic energy of an electron beam to work a material US. Patent No.3,009,050, issued November 14, 1961, to K. H. Steigerwald, disclosessuch a machine. These machines operate by generating a highly focusedbeam of electrons which is caused to impinge upon a workpiece. Theelectron beam is a welding, cutting and machining tool which haspractically no mass but which has high kinetic energy because of theextremely high velocity imparted to the electrons. Transfer of thiskinetic energy to the lattice electrons of the workpiece generateshigher lattice vibrations which cause an increase in temperature withinthe impingement area sufiicient to accomplish work.

In apparatus, such as electron beam machines, which use beams of chargedparticles to perform work, the elements which emit or otherwise causeproduction of the particles which comprise the beam are highlysusceptible to damage. For example, the electrons which form the workingbeam in an electron beam machine are emitted by a filament which isheated to an extremely high temperature. Any oxygen in the chamber wherethe filament is located will cause almost instantaneous oxidation andfailure of said filament. Thus, it is required that the filament belocated in an evacuated chamber. If the filament is located in anevacuated chamber, it has, in the prior art, followed that the workpiecemust also be located in an evacuated chamber. Because there arepractical limitations on the size of the evacuated work chamber andfurther because of the time-consuming operation of pumping down the workchamber for each new workpiece, it obviously would be highly desirableto locate the workpiece outside of the vacuum.

If the workpiece is positioned outside of the vacuum, means must beprovided to bring the beam, without attenuation, out of the low pressurechamber in which it is generated. This presents a second problemcoincident with the above-mentioned oxidation danger which, of course,arises because of the leakage of gas up the beam path. In applicationswhere it is desired to weld, drill or perform other operations thatrequire high beam power density, any gas molecules present in the pathof the beam will interact with the beam and substantially attenuate thebeam intensity through scattering caused by collisions between the gasmolecules and the beam particles. Therefore, in order to minimize thisundesirable attenuation, the length of the beams path along which thereis a heavy concentration of gas molecules must also be minimized. In theprior art, various schemes have been tried to overcome these twoaforementioned problems. However, to date, only moderate success hasbeen achieved and this only by the use of cascaded vacuum systemsutilizing large capacity, high speed vacuum pumping apparatus. Anexample of this approach is illustrated in the above-mentionedSteigerwald patent. A further variation of the cascaded vacuum system isthe use of a pressure stretch such as that disclosed in US. Patent No.2,640,948, issued June 2, 1953, to E.. A. Burrill.

My invention overcomes the above-stated problems and produces better andmore efiicient operation than previously obtainable by providing novelapparatus for permitting a beam of charged particles to be brought outof a low pressure chamber to a region of relatively high pressure.

It is therefore an object of my invention to provide communicationbetween a low pressure chamber and a region of relatively high pressure.

It is another object of my invention to bring a beam of chargedparticles out of a region of low pressure to a region of higher pressurewith a minimum amount of attenuation.

It is still another object of my invention to perform work with a beamof charged particles at atmospheric pressure without damage resulting tothe beam-generating apparatus.

These and other objects of my invention are accomplished by novelapparatus wherein a beam of charged particles is generated in anevacuated chamber and then accelerated through an aperture where itimpinges upon a workpiece which is positioned in a region of highambient pressure. The particularly novel feature of my inventioncomprises means for inducing a flow deflection, away from the beam axis,of the gas which attempts to rush into the evacuated chamber throughsaid aperture.

My invention may be better understood and its numerous advantages willbecome apparent to those skilled in the art by reference to theaccompanying drawing wherein like reference numerals refer to likeelements in the various figures and in which:

FIGURE 1 is a sectional view of a first embodiment of my invention.

FIGURE 2 is a cut-away view of a second embodiment of my invention.

FIGURE 3 is an enlarged partial view of the embodiment of FIGURE 2.

Referring now to FIGURE 1, there is shown an electron beam machinecomprising an electron beam column indicated generally at 10. In thiscolumn are located means, such as those shown in the above-mentionedSteigerwald patent, for generating an extremely high energy electronbeam. Column 10 is evacuated by thirdstage pump 12. The beam generatedin column 10 passes down a conduit 14 which is located between the coilsof a magnetic lens assembly 16. The function of lens assembly 16 is tofocus the beam at the workpiece which is positioned at a desireddistance below the lens. Upon emerging from conduit 14, the beam passesthrough -a chamber 18 which forms the second stage of a three-stagecascaded vacuum system. Chamber 18 is evacuated by a second-stage pump20. The beam exits from chamber 18 through second-stage probe 22 andthen passes through chamber 24 of the first stage. Chamber 24 isevacuated by first-stage pump 26. The beam leaves chamber 24 through anorifice 28. After passing through orifice 28 the beam strikes workpiece30 where, in accordance with its parameters as set by the operator, itperforms the desired type of work. Workpiece 30 is positioned upon amovable table 32 and is thus movable in respect to the beam axis. Asshould be obvious to those skilled in the art, the distance betweenorifice 28 and workpiece 30 must be kept as small as possible tominimize scattering or attenuation of the beam due to collisions betweenthe charged particles and molecules of air.

Because of the large pressure drop across orifice 28, the ambient air isinduced to flow up into the electron beam machine. The novel feature ofmy invention consists of means for turning this air. which flows intothe evacuated column through orifice or nozzle 28, away from the beamaxis thus minimizing both leakage into the region of column where thebeam of charged particles is generated and also the length of the pathof the beam along which there is a heavy concentration of air moleculeswhich would cause attenuation of the beam. To accomplish the foregoing,my invention utilizes the bistable valve principle. A passage 38 isformed in the bottom wall 34 of the first-stage chamber 24. Passage 38terminates in an opening 36 which is in communication with the ambientair. Passage 38 may be tapered at its other end to form a nozzle or jetvalve 40 having its longitudinal axis perpendicular to the beam axis.Nozzle 40 is shaped and sized so that the flow discharging therethroughmay be either sonic or supersonic depending upon the particularapplication. The bistable valve operates on the principle that there aretwo stable modes of flow for a given geometric configuration as, forexample, the one shown in FIGURE 1. The two stable flow modes for theair entering the evacuated regions through orifice 28 are straightthrough into probe 22 or to the side between wall 41 and airfoil shapedmember 42. The position or path which the flow assumes depends onwhether or not a side flow is induced in passageway 38 and throughnozzle 40. If, as in the embodiment of FIGURE 1, such a side flow isinduced, the main flow through orifice 28 will be turned and will passbetween wall 41 and member 42. Thus, the main flow will be deflectedaway from probe 22. By virtue of this deflection of the main flow, thesecond-stage probe 22 only feels the static pressure in chamber 24 anddoes not feel the dynamic pressure created by the main stream. It isapparent from the foregoing that the second-stage probe 22 is notsubjected to the total pressure head and consequently the air weightfiow at this point is not as high as it would be without my invention.As a result of the reduction of weight flow at second-stage probe 22,the required capacity for second-stage pump is significantly reduced.This affords a substantial savings in cost, consumption of power, andthe like. The use of this jet valve deflection also permits closespacing of probe 22 to orifice 28 and this close spacing, in turn,greatly reduces beam attenuation since the beam has a much shorterdistance to travel through partially evacuated or unevacuated regions.

Referring now to FIGURES 2 and 3, there is shown a second embodiment ofmy invention wherein the deflection of the gas attempting to flow intothe evacuated electron beam machine is achieved by an aerodynamic nozzlepressure staging device. In FIGURES 2 and 3, the charged particlegenerator, like that discussed above in relation to the embodiment ofFIGURE 1, incorporates a staged vacuum system comprising first-stagechamber 24, second-stage chamber 18, and the beam forming column 10which functions as the third stage. As in the embodiment of FIGURE 1,the ambient air in the region of workpiece attempts to rush into theevacuated region through orifice 28.

As is well known in the art, when air rushes through an orifice withvery low downstream static pressure, the flow will be supersonic andbehave as a free-stream jet discharging into a large chamber. Because ofthe low downstream static pressure, the air will compress and expand ina predetermined pattern causing shock waves and expansion waves to beformed. As a result of this wave pattern, a series of minimum pressurepoints are established. By locating a second-stage probe, such as 22, atone of these points of minimum pressure, the mass flow into asecond-stage chamber may be decreased. This manner of locatingsuccessive probes at minimum pressure points in a free jet flowing intoa cascaded vacuum system has previously been utilized as shown in US.Patent No. 2,899,556, issued August 11, 1959, to E. Schopper et al. Myinvention constitutes an improvement over the prior art in that itdeflects the flow entering a low pressure chamber through an orificeaway from the axis of the second-stage probe and in so doing can producea lower pressure at the tip of the probe than previously obtainable.

My improvement consists of shaping the outside wall of second-stageprobe 22 and the inner wall 44 of a passage forming member 46, extendingfrom the downstream side of orifice 28, to define a diverging nozzle 48.That is, probe 22 and wall 44 are shaped so that section 48, which theydefine, forms the divergent section of a convergent/divergent nozzlehaving its throat at orifice 28. By proper sizing and location of nozzle48, as shown in FIGURES 2 and 3, and proper adjustment of the staticpressure in first-stage chamber 24, flow is directed therethrough and anormal shock wave 50 is formed between second-stage probe 22 and innerwall 44 downstream of the tip 52 of probe 22. Thus, the shock is locatedas shown in FIG. 3 by proper matching of the design of nozzle 48 and thecharacteristics of pump 26. For a given design of nozzle 48, thismatching is accomplished by varying the pump flow until the shock islocated at the desired point. The normal shock wave drops the velocityof the air passing through nozzle 48 from supersonic to subsonic therebyrealizing an increase in static pressure in first-stage chamber 24 whilea very low static pressure is maintained just before tip 52 of probe 22.This affords an advantage over the prior art in that for a given staticpressure in first-stage chamber 24, the static pressure just upstream ofsecond-stage probe 22 is much lower than in a free jet type apparatus asexemplified by the above-mentioned Schopper et al. patent. This is dueto the greater expansion or turning of the air passing through orifice28 made possible by properly shaping the wall 44 instead of allowing theair to expand as a free jet whose surface pressure would be the staticpressure in chamber 24. This lower static pressure therefore results inreduction of the weight flow to the second-stage chamber 18 and therebypermits a reduction in the size 0f second-stage pump 20. Conversely, ifit is desired to maintain the size of pump 20 equal to that utilized inthe prior art, then a significant reduction in first-stage pump size canbe realized with this embodiment of my invention because there is a risein pressure across the shock wave 50 which accomplishes some pumpingaction, thereby reducing the pumping requirement of the first stagepump. By proper design of probe 22 and wall 44, it is possible to reducethe size of both first and second-stage pumps as compared'to the pumpsemployed in the prior art devices and yet obtain the same overallperformance.

While a preferred embodiment has been shown and described, variousmodifications and substitutions may be made without deviating from thescope and spirit of my invention. Thus my invention is described by wayof illustration rather than limitation and accordingly it is understoodthat my invention is to be limited only by the appended claims taken inview of the prior art.

I claim: 1'

1. Apparatus for working materials with a beam of charged particlescomprising:

a first chamber having a beam exit aperture,

means positioned in said first chamber for generating a beam of chargedparticles,

means for evacuating said first chamber,

means supporting a workpiece outside of said evacuated first chamber ina gaseous atmosphere,

means positioned adjacent the aperture in said first chamber forpermitting passage of the beam from said first chamber to the workpieceregion without material attenuation, and

means positioned between the termination of said passage permittingmeans and said workpiece for inducing a flow deflection away from thebeam axis of the stream of gas which tends to flow into the evacuatedfirst chamber from the region of the workpiece. 2. The apparatus ofclaim 1 wherein the means for inducing a flow deflection comprises:

means establishing a jet of deflecting gas which impinges against andthus turns said gas stream. 3. The apparatus of claim 2 wherein themeans establishing the deflecting jet comprises:

means including at least a second chamber positioned between thetermination of the passage permitting means and the workpiece, meansaligned with said passage permitting means for permitting the beam toenter said second chamber, means in the wall of said second chamberlying adjacent the workpiece for permitting the beam to pass out of thesecond chamber to impinge upon the workpiece, means for evacuating saidsecond chamber, means providing communication between the atmospheresurrounding the workpiece and the interior of said evacuated secondchamber for inducing a flow of deflecting gas in said second chamber atan angle to the beam axis. 4. The apparatus of claim 3 wherein the meansfor inducing a flow of deflecting gas comprises:

a passageway through a wall of said second chamber, said passagewayhaving its discharge end located in the second chamber, said dischargeend having its longitudinal axis in angular relation to the beam axis.

5. The apparatus of claim 4 wherein the means for permitting the beam toenter the second chamber comprises:

a hollow probe positioned so as to be coaxial with the beam axis andextending into the second chamber to a point adjacent the means forpermitting the beam to pass out of the second chamber.

6. The apparatus of claim 1 wherein the means for inducing a flowdeflection comprises:

means including at least a second chamber positioned between thetermination of the passage permitting means and the workpiece,

means aligned with said passage permitting means for permitting the beamto enter said second chamber,

an opening in the wall of said second chamber lying adjacent theworkpiece for permitting the beam to pass out of the second chamber andimpinge upon the workpiece,

means for evacuating said second chamber, and

means extending from said opening in the downstream direction of the gasentering the second chamber from the workpiece region through saidopening for causing expansion of the entering gas.

7. The apparatus of claim 6 wherein the means for causing expansion ofthe gas comprises:

a contoured wall extending from said opening into said second chamber,said wall being coaxial with the beam.

8. The apparatus of claim 7 wherein the means for permitting the beam toenter the second chamber comprises:

a hollow probe extending into said second chamber to a position where itis coaxial with the beam and contoured wall whereby said probe andcontoured wall together form a nozzle.

Steigerwald Feb. 18, 1958 Schopper et al. Aug. 11, 1959

1. APPARATUS FOR WORKING MATERIALS WITH A BEAM OF CHARGED PARTICLESCOMPRISING: A FIRST CHAMBER HAVING A BEAM EXIT APERTURE, MEANSPOSITIONED IN SAID FIRST CHAMBER FOR GENERATING A BEAM OF CHARGEDPARTICLES, MEANS FOR EVACUATING SAID FIRST CHAMBER, MEANS SUPPORTING AWORKPIECE OUTSIDE OF SAID EVACUATED FIRST CHAMBER IN A GASEOUSATMOSPHERE, MEANS POSITIONED ADJACENT THE APERTURE IN SAID FIRST CHAMBERFOR PERMITTING PASSAGE OF THE BEAM FROM SAID FIRST CHAMBER TO THEWORKPIECE REGION WITHOUT MATERIAL ATTENUATION, AND MEANS POSITIONEDBETWEEN THE TERMINATION OF SAID PASAGE PERMITTING MEANS AND SAIDWORKPIECE FOR INDUCING A FLOW DEFLECTION AWAY FROM THE BEAM AXIS OF THESTREAM OF GAS WHICH TENDS TO FLOW INTO THE EVACUATED FIRST CHAMBER FROMTHE REGION OF THE WORKPIECE.